Three sets of medically important yeasts, Candida albicans, C. tropicalis, and C. krusei were compared with their putative synonyms (C. langeronii and C. clausenii; C. paratropicalis; Itsatchenkia orientalis) to determine if these synonyms are genetically distinguishable from each other. Molecular techniques used to accomplish this goal included pulsed-field electrophoresis and hybridization to species-specific probes. This study did not identify any distinguishing characteristics between synonyms, thus supporting the current taxonomic treatment of these pathogens. Diverse karyotypes were found for Kluyveromyces marxianus var. marxianus which is the sexual state of Candida kefyr. Two distinct karyotypes were discernable among the strains isolated from various sources. The enzyme profiles, however, showed great similarity and the majority of enzyme patterns did not vary. The enzyme profile was stable over the maintenance of the cultures while the karyotype was unstable due to the frequent chromosomal rearrangement.